(Variable) Noise Generator complete!

This morning I completed my second noise module.  The one I did previously had a switch to go between white and pink nose, this one uses a pot as a cross-fader between the two. The PCB and all components are the same, it is just a matter of connecting a pot to one header, or a switch to another.

It has been a while since I used my other noise module, so I can't do an A/B comparison quite yet.  But, yes, it does sound noisy. ;-)  I also just used one transistor, and didn't try a few and choose my favorite.  (I thought about it, but oh well!)  The sound is interesting with the cross-fader.  Turning it to the right is a bit like lowering the frequency on an LPF (with white noise input), but not quite.  It gives some interesting flavors of noise at middle settings.

My Input Amplifier and Tuner/Monitor are so close to being finished, but I'm cursed with missing about $0.80 worth of panel parts.  I also have boards to build some more of other modules, but those are competing with my 3-panel Best Of CGS build... most likely I'll jump back and forth.

Voltage Processor/Mixer complete!

Wow, has it seriously been 4 months since I last updated this blog?!  Things have been a bit of a roller-coaster here, but I'm finally getting back into this project.

Today I finished assembling the Voltage Processor/Mixer module.

It is a fairly straight-forward build, though with a number of jacks.  (Nothing nearly as complex as the Selective Inverter, however!)  I tested it and everything works great - the attenuated inputs amplify as well, which is a nice plus!  As with the S.I., the offset voltage is bipolar and doesn't center at zero (due to the +12V/-10V supply), so just bear that in mind with testing so that you don't confuse yourself like I initially did with the S.I.  (There's a reason why the switch is there!)  It should be interesting to play around with this one, with the various inversions and summings.

In the meantime, I'm finishing up a few other modules (Noise module with white/pink pot, Input Amplifier, and Tuner/Monitor - just waiting on a few parts), and should have PCBs in soon for some more VCOs, VCAs and VCFs.  In addition, I'm also getting everything together to (finally!) get everything together in a cabinet... the small rack I have has just been more of a pain than anything, and I really never got much set up in it!

Sequencer complete!

The sequencer is now ready!!  It is quite a dense and heavy beast...

Oops, there's a few bits of wire insulation that got stuck to the knobs. ;-)

As I mentioned, I didn't solder in the UJT initially, but just set it in there, in case there was any issue with it at high frequencies.  Tested it, and it worked fine on the first try!  (Well, I had two switches upside down, but it only took a couple minutes to fix those.)  So, I soldered in the UJT from the top, and just left the legs hanging down... no big deal.

I've mostly just played around with the clocking mechanism, but everything seems to work fine elsewhere too and it is really interesting.  The RYM (3rd row control of timing) is fun, as are the different modes. 

Now, if only the screws to mount these modules to the rails would finally arrive here(?!?!), I could get everything working together!

Selective Inverter complete!

And now, the Selective Inverter is finished!

It is a really crowded build.   Getting the banana jacks on there was tough, as the nut drivers didn't cut it - I had to use pliers to get the nuts tightened.  (Of course, that's what I get for having all those multed jacks in a banana system!  But, I don't mind.) 

One thing that I didn't realize from the description, but suspected from the schematic, was that in the fixed mode the "B" output is always inverted (i.e. the trigger inputs do nothing).  Also, I was really confused at first while testing it, until I remembered that the offset voltage is bipolar (-10V to +12V).  Anyhow, I'm very much looking forward to trying this out with some "real-world" applications!

Frequency Divider complete!

And now the Frequency Divider is done! Sorry the pics aren't so great, but the sun never came out today...

As you can see, I've used some washers as spacers on the rotary switches - otherwise they protrude too far.  I've used some rather long standoffs to accommodate the Alpha rotary switches.

I haven't played around with it too much, and even then only with the oscilloscope, but it seems like a really interesting module which can perform not only suboctave divisions and clock divisions, but can also mix said suboctaves and produce staircase style sequences like the CGS Suboscillator/Harmonic Sequencer and the Blacet Binary Zone.

In other news, I've got panels here for both the Selective Inverter and Sequencer, and the boards are almost complete, but unfortunately I am missing one capacitor for each!  Hopefully I'll have those shortly, and get them finished up.

Triple Envelope Generator complete!

Sorry, it has been quite some weeks since I last updated this blog!  I've been on jury duty for a major trial, with no real end in sight.  Trying to juggle that with work is a bit of a headache, to say the least...

At least I've managed to work on my Synthasystem a bit during this time, including completing the Triple EG.

Clearly, there is a ton of wiring on this module!  Four PCBs and 28 panel components, of which most are pots and switches.  Initially EGs 1 & 3 worked fine, but EG 2 would only produce a gate output (i.e. Attack/Decay had no effect), but after some debugging I figured out that the pad on the 3.9u tantalum cap got lifted or something - I put a quick jumper wire across to fix that; not the prettiest fix, but it certainly works!

It runs on just the +12V rail, and (as the name suggests) contains 3 envelope generators.  The first two are quite similar: something of a cross between an ADSR and an AD/AR envelope, with some interesting modes.  The second one also allows the Attack knob to act as a delay.  The third EG is more of an AD/AR envelope, with a "hold" time (similar to the Korg MS-10, etc.) that can be used instead of the input trigger's duration.  The third envelope can also be summed into either of the first two envelopes.

I like the fact that the envelopes are much simpler to control, compared to traditional ADSRs, which I sometimes find to be a bit of a pain to adjust on the fly.  I'm hoping that these will fit my needs a lot better (and I think they will).

I'm hoping to get everything set up fine in my rack soon... I really just need to make some power cables, and get some screws to install the modules.  I hope to make some demos of this (and other modules) soon after!

Phase Shifter complete!

And the phase shifter is now complete, too!

A fair amount of op-amps in there!  It is a 4-stage, 720-degree phaser. There's a wet/dry knob to control a mix of the original signal & the phase shifted signal, which is ideal for effects.  I only tested it lightly, but it seemed that the frequency knob didn't do much above 2:00 - perhaps it was just due to the setting of the original waveform, as it clearly did a lot to the signal before it got to 2:00!  There's a VC input for this too, but I haven't played with it yet - since it is summed with the frequency knob, however, it should work just fine.

Ring Modulator complete!

And, the Ring Modulator has also been completed!

This uses an MC1495 IC (four quadrant multiplier), which is certainly a more frequently encountered solution (with a variety of different chips & circuits) than the diode "ring" design.

It has a couple of trimpots, for the Signal Null and Carrier Null... they're pretty simple to set.  Obviously the one is on the front panel, but I'm not sure why, i.e. if it needs more frequent adjustment or what.  There's also a pot to adjust the mix of original signal to modulated signal, which could prove interesting to play with.

While I'm at it, let me admonish the reader to watch out for those blue plastic panel-mount trimpot assemblies.  The threads are very prone to being stripped, and, as they're plastic (and have some flashing), they're quite easy to strip if you're not careful (and sometimes even if you are careful... oops!).

And finally, there's a Mult/Square switch.  In the multiply position, it acts as a standard ring modulator.  However, in the squared position it sends the signal input to the carrier input too... honestly, I'm not sure why this wasn't originally implemented with a normalled jack (as they're used in other situations in the Synthasystem), but no matter - for me it'll save a banana cable!  Theoretically I think it is supposed to double the frequency, but instead it just seems to change the signal a bit.  I honestly haven't played around with this a whole lot (mostly just setting the trimmers), so I'm sure there's quite a bit to discover.

Peak Selector complete!

Here's the completed Peak Selector module.

Another fairly simple build. I now feel a lot more comfortable wiring up LEDs. This is basically just a comparator that outputs an S-Trigger (and lights an LED) whenever the input exceeds the set threshold.  However, it isn't done with OpAmps, so (to me) it is a bit more confusing, circuit-wise.  It has a minimum on-time, which seems useful, but means that if you want to feed it noise, you'll have to do so through a sample & hold or something - otherwise the output will be on all the time.

In the meantime, I also ordered a panel for the Triple EG yesterday... I tried to order all the panel parts too, but I'm afraid that I forgot some of the MTA connectors for the power - aaah!!  There's always one thing I forget whenever I place a Mouser order...

Noise Generator complete!

Here's the completed Noise Generator module!

Simple panel assembly; just a pair of jacks, a level pot, and a white/pink switch.  The next one I do will have the pot to go between white and pink.  Sounds great!  And works like a charm.

VC Oscillator complete!

I've now completed one of my two initial VCOs.

As you can see, there's a lot of wiring! I've added the HF compensation board, which gets wired down to three points on the main PCB. It is indicated on the schematic, and some good quality photos that David has on his site. (Of course, ground can go to many places, but I just chose one that was easy.)

The calibration is pretty extensive for this module. First the waveforms need to be calibrated: first the saw, followed by the pulse, triangle, and sine.  Then the 1V/Oct tracking, and then the frequency range.  This is documented on the build pages.  I've done all on this module, but will go over it again just to get things as precise as possible - I just did a quick setup of the tracking, for instance.  One thing to note on the waveform calibration is that if you see truncated waveforms, be sure to check the DC offset for that waveform.

Unfortunately, my second VCO isn't going so well, at least where the sine wave is concerned.  There's two settings of the trimmer where you get a sine wave, and only one is correct.  (The incorrect one has a very high point-to-point voltage!)  I've managed to get to both of them, but haven't managed to get the trimmer settings right.  (Or there's something wrong!)  A bit frustrating staring at a scope and holding the module awkwardly and turning the trimpots.  (I really ought to power this on my bench, rather than out of my Dotcom modular...)

Once I have it working, though, I'll share any further tips... plus oscilloscope shots!  Hopefully I'll have some time this weekend, though all of Sunday I'll be up in Anaheim at NAMM.

In the meantime, I've been working on the power supply & distribution panel, which I'll share shortly.  Additionally, I've ordered PCBs for the Noise, Peak Selector, Ring Modulator, Phase Shifter, Triple EG, and Frequency Dividers.  All the board parts are on-hand, so putting those together should go rather smoothly!

VC Filter complete!

And now, the VC Filter is also completed!

Like the VCA, this also has a CV Reject trimpot. I ended up having to adjust it the same way - fully CW - to minimize (but not eliminate) VC bleed into the output.  I did a few audio tests, and it sounds really nice!

I used one of the Electroswitch rotary switches, and I must confess that I don't really like it... it feels very "mushy" to turn - you don't get a solid "click".  I'll want to find something else for future modules, and eventually replace the one here.

VCA/Mixer complete!

The VCA/Mixer module is now finished!

Aside from the pull-down resistors previously mentioned, it was pretty easy to assemble to the panel.  There's only one trimmer on this module, which is the CV Reject for cutting down on CV bleeding to the output. I sent the VC inputs an audio signal from a VCO, and could eliminate most, but not all, bleed, by turning it fully CW. Everything seemed to work fine in testing.  Note that this uses linear pots, so you may not get the typical response you may expect from VCAs that use log pots.

Voltage Follower All Done!

And the last of my first 3 modules to be completed is the Voltage Follower.

Simple circuit and simple interface.  I tested both circuits using the S&H as input, and it worked fine.  This is an exponential slew (or lag, portamento, etc.).  I don't know why the term "Voltage Follower" was used for that, as I've only seen it used before for a unity-gain buffer. Though, I guess this has four voltage followers in it (more OpAmp buffers than in any other Synthasystem module, I believe).

I haven't tried to see what the max lag time is here, since it is obviously a bit tough using random input from the S&H, combined with the exponential response.

Sample & Hold Complete!

Although I finished this (and the Voltage Follower) before I got the VC Trigger Generator working, I decided to wait until the latter was functioning before I posted these.  Here's my completed banana-fied S&H!

Things are a bit crowded on the front panel with the switches, but I figure that the switches & knobs on the S&H aren't used a whole lot once a patch is set up.  (At least based on my experience with other S&H units.)  I took off the large tabbed washers from the NKK switches, because they protruded just slightly from the edges.  Obviously I could've ground them down, or just made sure to put the S&H in the cabinet first, but they aren't critical, so it didn't seem worth it.

No calibration is required on this module, and both circuits worked just fine.  I've tried triggering it from the VC Trigger Generator, and even just a banana cable connected to ground.  The grounded banana was a bit wonky, since the input isn't debounced, and you'll accidentally trigger it 2-3 times - but it worked!  I initially tried testing it with my DMM, but the output wasn't steady at all (I'm not sure why) - everything showed up fine in the oscilloscope, though.

You'll notice on this (and the VC Trigger Generator) some of the MTA headers are unused - those are for the V-Triggers that I'm not using.

The boards are designed to be used with switching jacks for the inputs, with the switch lug attached to the internal "noise" generator.  I've used a SPDT switch instead, with common attached to the signal input, and the ends attached to the internal "noise" generator and the jack, respectively.  I didn't try it with an external signal, but considering it works from an internal source, there shouldn't be a problem.

I've called it the "internal 'noise' generator" because (to my surprise) it isn't actually a noise generator!  Instead, it is actually a ramp oscillator (based off of a UJT) running at approximately 12kHz. It is going fast enough where you'll get something that is effectively random. There's two of these on-board, with one for each S&H, which is nice, so you won't have the output correlated between the units.

VC Trigger Generator: Done!

Success at last! I got the VC Trigger Generator working, finally.

The culprit ended up being the UJT. However, given that this was a $10 part, I wanted to make certain that it was at fault before replacing it!  David Ingebretsen helped me with understanding and debugging this circuit - thanks so much!  I learned a lot in doing it too.  Lots of measuring voltages at various points, particularly transistor bases.  Eventually figured out which blocks were working, and which weren't. Narrowed it down to the UJT, popped it out, put a new one in, and presto!!

Calibration was a bit of a pain, due to the fact that I'd moved the trimpots all around, but it was all set after about 5-10 minutes in front of the oscilloscope.  The Duration/Width pot was working the opposite way of how I'd expected it to work, with 10 being the smallest pulse, and 0 being the widest. Apparently this is how David's works as well, it is how it is noted in the schematic, and Nyle didn't notice anything odd with David's unit... so presumably it is how it is supposed to be?  Anyhow, it seems a bit odd to me, so I switched the MTA and reversed it.

Another oddity is the fact that at rest it outputs approx 10V, rather than floating - this is due to the way that the LED is set up. On its own this isn't a problem, but I am a bit concerned about OR-ing trigger signals from these modules.  It doesn't look like it should be an issue with the other trigger generators (i.e. the Sequencer and Peak Selector).

Also, note that I didn't screw the PCB down all the way onto the top two standoffs - the pushbutton switches are rather large, and push against the board.  If I were to do it over, I'd just put the wires going to the pushbuttons going off to the side, rather than straight out.

It really has a lot of range - I didn't measure it, but with the range knob at 12:00 the pulses have a period of 85ms, and from that it goes really fast, and really slow.  I didn't try the 3 inputs yet, but given the circuit and that everything else works, those should work without issue.

A great way to start the new year by getting this working!